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How To De-Anodize?

We manufacture some automotive parts out of AL7075-T7352 and we coat them with the use of an anodizing process for rust prevention. During the process of anodizing the anodized surface loses its color and we have found some spots on the surface of the component. Now we want to de-anodize so that we could do the anodizing again. How can this be done!?

Thanking you,

Mirza Habib Ullah
Machine Shop Foreman - Lahore, Pakistan
2004

In order to strip the anodic coating, the easiest method would be to use a chromic acid/phosphoric acid solution. the make up of this solution is as follows: make up 1 litre of solution by adding the following to DM water. 55 mls / litre phosphoric acid 20 grams / litre chromic acid.

Heat this solution to 98 degrees C or boiling, and immerse the parts for 5 - 10 minutes, and this will strip the anodic coating.

Stuart Haynes
Surface Treatments - Manchester, England
2004

Hi Mirza. But remember where the aluminum in that anodized coating came from: the substrate. If you strip .002" of anodizing, the part will have .001" less aluminum than when you started.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2013

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